This invention relates to a flow regulator. More particularly, this invention relates to a flow regulator of the type which compresses a tube to vary a flow rate of a fluid passing through the tube. Even more particularly, this invention relates to a flow regulator of the roller type. The invention is useful in medical applications, to control the flow rate of intravenous fluids, parenteral fluids, blood, plasma, etc.
Intravenous tubes have been widely used for supplying nutrients and medication to patients. Most existing manually adjustable clamps for regulating the flow rate through an intravenous tube have a high degree of inaccuracy, particularly after the clamped tubing has been in use for a period of time in excess of one hour. In addition, existing manually actuated clamps cannot be used where the fluid being delivered through the tubing is viscous, for example, blood. If a substantial degree of accuracy in flow rate maintenance is required, it has been necessary to utilize an expensive pump system. Even pumps systems are limited in their accuracy.
A particularly common kind of flow regulator in medical applications is the so-called Adelberg clamp which uses the combination of an inclined plane or V-grooved surface and a roller that is moved along the inclined plane or grooved surface to variably compress the tube to allow more or less liquid to flow through the tube. Although widely used, the Adelberg clamp is less than ideally accurate and reliable, so as to require continual monitoring and adjustment to maintain a desired flow rate. The position of the roller is easily shifted in the V-grooved and ramped versions since the clamp design has not taken into consideration the direct effect of stress and strain as a critical contributing factor in maintaining an accurate and consistent flow rate through the roller clamp.
An object of the present invention is to provide an improved manually adjustable flow regulator of the above-described roller type.
Another object of the present invention is to provide a manually adjustable flow regulator which has enhanced accuracy and reliability.
An additional object of the present invention is to provide such a flow regulator which is inexpensive and easy to manufacture.
A further object of the present invention is to provide a manually adjustable flow regulator which is utilizable where a medical fluid is to be delivered through a flexible tube.
These and other objects of the present invention will be apparent from the descriptions and illustrations herein. It is believed that each of the above-described objects is achievable in one or more embodiments of the invention described herein.
A flow regulator comprises, in accordance with the present invention, a pair of side walls extending generally parallel to one another, a bottom wall connecting the side walls to one another and defining an elongate channel for receiving a compressible tube, a roller rotatably and shiftably mounted to the side walls for rolling along the tube in the channel and compressing the tube against the bottom wall. The bottom wall is provided with a formation which varies from a first end of the channel towards an opposite, second end thereof, whereby a compressive force applied to the tube via the roller is different at different longitudinal positions of the roller along the channel. A reinforcement bracket is disposed about the side walls at one end of the channel. The bracket is in contact with outer surfaces of the parallel side walls only in regions of the side walls spaced from the bottom wall. In a different embodiment, the bracket is replaced with a bridge of relatively flexible construction spanning the two side walls, disposed at the flow regulator shut off end. Advantageously, the side walls and a bottom wall, including all parts of the clamp with the exclusion of the bracket or bridge, are made from a material more rigid than the material from which the bracket or bridge is made.
As suggested above, prior V-grooved or ramped roller clamps suffer from setpoint drift attributable to shifting of the roller position. The prior clamp structures are not believed to have taken into adequate consideration the direct effect of stress or strain as a critical contributing factor in degrading an accurate flow rate performance of the roller clamp. The relationship of a stiffness of the bridge to the flow regulator chamber or channel walls, as well as the contributory factor of differences in intrinsic elasticity of the materials used for component manufacture are critical in maintenance of accurate device performance. The present invention describes an effective method of taking cognizance of stress and strain in the device, and controlling these factors for optimum performance.
U.S. Pat. No. 5,718,409 to the same inventor implicitly dealt with stress and strain in a roller clamp by introducing a reinforcing bracket to an existing design. In further tests of similar devices it has become evident that modifying the flexibility or stiffness relationships between the chamber walls and the bridge or bracket component further improved the accuracy and consistency of the device, by limiting the flexing of the side walls and simultaneously reducing a strain state of the bridge or bracket.
U.S. Pat. No. 5,718,409, the disclosure of which is incorporated herein, shows a bracket contacting the outer surface of the sidewalls of the roller clamp body at a shut-off or maximally restricted flow end of the device. In the prior art, the roller tended to roll towards the shut off end during operation of the clamp. The movement is presumed to have arisen as an effect of operating stresses in the interrelated parts of the roller clamp assembly. As the roller pinches the tube, pressure is generated on the plastic walls of the device. This pressure causes an end of the clamp to flair open to various degrees, depending on a position of the roller. In order to control the effect of stress on the device, structure defining the roller clamp chamber requires a more rigid material construction. The elastic relationship of the roller clamp chamber structurexe2x80x94comprising parallel side walls and bottom wallxe2x80x94to the bracket or bridge structure is an important design parameter, as the two parts structure interact to accommodate the varying stresses resulting from different roller setting in the operating device.
The bracket previously described in U.S. Pat. No. 5,718,409 serves to maintain flow constancy by controlling a change in a gap distance between the parallel side walls of the roller clamp, engaging the walls predominantly at the shut off end. Simultaneously, the bracket provides the side walls with a controlled springy effect which means that, as the roller starts to roll towards the shut off end, the controlled springy flexibility of the walls will respond to the roller""s tendency to roll down; at times when the amount of fluids delivered lessen, it would cause a decrease in the degree of stress and strain between the bracket and the chamber, and the pressure between the roller and the tube where the roller might otherwise change its position, with bracket feature on the clamp the roller will be held constant by the springy effect of the parallel side walls. After this discovery was initially made by the inventor by numerous in-house tests and several official laboratory tests, improvements were made in the design which make this device easier and less expensive to manufacture, while maintaining the original objectives of maintaining superior and constant flow regulating. These improvements result in a device having a predetermined and controlled elastic performance relationship during stress effects which involve the entire assembly.
The bracket or bridge is preferably disposed at the end of the flow regulator where the tube is subjected to the greatest compressive forces and the controlled flow rate is the lowest. The bracket prevents an undue flexing of the side walls away from each other under forces exerted by the roller and the compressed tube. In one version or embodiment of the present invention, the bracket mounts around the parallel side walls and the bottom wall connecting the parallel sides. In another version, the bracket fits over the parallel side walls only, at the shut off end of the clamp. In yet another version, the bracket is mounted in such a manner that it interfaces with the bottom wall and the side walls and the bracket clips over the top edge of the side walls, leaving a section of a gap between the parallel side walls open. The thickness of the bracket ends is sufficient to stop the roller from accidentally rolling past the end of the channel housing.
In accordance with a feature of the present invention, it is contemplated that the side walls at the bracketed end of the channel are connected to one another only by the bottom wall at one side and the bracket at an opposite side. Thus, a web or strut which extends between the side walls at the low-flow-rate end of a conventional regulator is omitted.
The bracket is made of a less rigid material, or exhibits less stiffness or resistance to bending, than the walls of the flow regulator chamber or channel. In another version or embodiment of the present invention, the bridge, also made of a less rigid material than the bottom wall and sides walls of the roller clamp, is disposed between the side walls at the shut off end of the flow regulator. This bridge has a curved formation of a bow like structure. This convex formation of the bridge points away from the shut off end and in opposite direction from the open end of the flow regulator.
Pursuant to another feature of the invention, the bracket includes portions spaced from the side walls in a region about the bottom wall.
In a specific embodiment of the present invention, the bracket is substantially U-shaped, with legs having free ends provided with fingers contacting the bottom wall. The fingers are substantially collinear and oriented towards one another.
In accordance with a further feature of the present invention, the side walls are provided along inwardly facing surfaces with respective grooves, the roller having a pair of shaft elements extending laterally in opposing directions along an axis of the roller, each of the shaft elements being provided at a free end with a friction enhancing formation. The friction enhancing formation may take the form of knurling, a layer of high friction material, embedded grit particles, or a series of axially extending ridges and interleaved longitudinal grooves.
In accordance with a yet another feature of the present invention, the flow regulator further comprises a pointer member coupled with the roller to move therewith as the roller negotiates the channel. A series of marks are disposed along the outer surface of one of the side walls for cooperating with the pointer to provide an indication of flow rate.
In accordance with an additional feature of the present invention, at least one of the sidewalls is provided with a seat receiving the bracket. The seat may be defined by a recess in the side wall or a shoulder on the side wall. The seat assists in retaining the bracket on the regulator.
The bracket may be bonded to one or both of the side walls, for example, by ultrasonic welding.
In a specific embodiment of the invention, the reinforcement bracket includes a first U-shaped portion spanning the channel on a side thereof opposite the bottom wall of the flow regulator and disposed in contact with outer surfaces of the side walls only in regions of the side walls spaced from the bottom wall. In this embodiment, the reinforcement bracket further includes a second U-shaped portion partially surrounding the first U-shaped portion, the second U-shaped portion having legs extending generally parallel to and spaced from the side walls of the flow regulator, the legs having free ends provided with fingers disposed in contact with the first U-shaped portion.
A manually adjustable flow regulator in accordance with the present invention provides substantially enhanced accuracy and reliability. The improved performance results from the addition of a single part to existing roller-type clamps. Accordingly, the flow regulator of the present invention is inexpensive and easy to manufacture. A manually adjustable flow regulator in accordance with present invention is utilizable where a medical fluid, for example, a parenteral solution, saline, plasma or blood, is to be delivered through a flexible tube.
In another feature of the present invention, it has been determined by experimentation that an unexpected benefit is accrued in terms of flow stability if the pair of side walls and bottom wall defining the elongate channel are manufactured utilizing material and dimensions creating a relatively stiff profile, while the bracket is manufactured using material and dimensions resulting in a relatively flexible reinforcing bracket or clip anchoring the side walls. Since one of ordinary skill in the art would likely have thought it desirable to make all components as stiff as possible to limit shifting of the roller, the relative advantage of a less stiff bridge or bracket part is an unexpected result.
An improvement made here over U.S. Pat. No. 5,718,409 accordingly originates in an observation that the rigidity or flexibility relationship between the chamber walls and the bracket (or bridge) is a significant feature in controlling performance of the flow clamp device. In specific embodiments of the present invention, the bridge or bracket is more flexible in its structure than the roller clamp chamber housing.
In accordance with a further feature of the present invention, the side walls and the bottom walls are made of a substantially less flexible material than the bracket or convex bridge are made of.
A manually adjustable flow regulator in accordance with the present invention provides an enhanced accuracy and reliability. The improved performance results from a substantially rigid chamber housing and a less rigid bracket or bridge assembly in a roller-type clamp. By incorporating these improvements a flow clamp device will prove easier and less expensive to manufacture, while yet advantageously maintaining desirable critical features of the device previously disclosed in the referenced patent, the matter of which is incorporated herein.